Immunosensors target analytes

Immunosensors have been designed which use both direct and indirect immunoassay technology to detect specific analytes within a minute or less in a variety of matrices (see Fig. 9). Indirect immunosensors may employ ELA, FLA, or CLIA principles whereby enzyme-, fluorophore- or chemiluminescent-labeled analyte competes with the target (nonlabeled) analyte for binding sites on the immobilized antibody. Unbound (free) labeled analyte is then quantitated using an electrochemical, optical, or electromechanical transducer and compared to the amount of target analyte in the sample. 

Due to the vast achievements in immunosensor development, only few highlights of novel immobilization techniques and investigative detection principles based on electrogenerated polypyrrole films are presented with cholera toxin and hepatitis C Virus (HCV) as exemplary target analyte. 

Pseudohomogenous amperometric displacement immunosensors have also been developed. The displacement assay is performed on a disposable screen printed carbon electrode and takes advantages of the cross-reactivity of some monoclonal antibodies. As an example, the monoclonal anti-2,4-D antibody exhibits a relative cross-reactivity toward immobilized MCPA. In the presence of the target analyte (2,4-D) a displacement effect is observed. Consequently, the peroxidase label of the remaining anti-2,4-D antibodies is detected at the carbon electrode, when adding hydrogen peroxide and potassium iodide as redox mediator, at OV versus Ag/AgCl. 

MPCs functionalized with large biomolecules including proteins, enzymes, and antibodies (immunosensors) are also abundant in the literature. A Ti02 nanotube array was decorated with antibody-labeled Au MPCs to allow for binding with a target analyte and amperometric detection. Typically, sensors must achieve detection limits of at least ng mL" to be a viable sensing platform for low-abundance proteins, and this sensor could lead to detection limits as low was 0.01 ng mL". Similar to the vast improvement in sensitivity for the chemiresistor that IDA electrodes made, miniaturization of electrodes into high aspect ratio arrays for this sensor led to enhanced electrochemical detection in comparison to flat electrode surfaces by 10-fold. ... 

An increasing number of immunosensors have been utilized to analyze a series of biochemical targets for diagnosing infectious diseases, although there are still problems concerning the assay of analytes in real sample matrixes [1]. 

---